Technical Abstract:
Symptoms for Citrus tristeza virus (CTV) were evaluated in Mexican lime, sour orange, Madam vinous sweet orange and Duncan grapefruit seedlings, and sweet orange plants on sour orange rootstock that were graft-inoculated with 267 different isolates of CTV originating from 30 countries. A series of 12 month tests were conducted over 16 years in a USDA-ARS quarantine facility at Beltsville, MD. Two standard isolates were included in each test to ensure that conditions and ratings were consistent. Plants which remained symptomless were tested by ELISA to verify infection. Symptoms induced by different CTV isolates varied markedly in severity under these uniform test conditions. The differences in severity were generally consistent with prior field observations and glasshouse indexing tests in other locations. Different symptoms patterns among the five indicators suggest that seedling yellows, the decline syndrome in sweet orange grafted on sour orange, stem pitting in sweet orange, and stem pitting in grapefruit are independent expressions of CTV pathogenicity and may occur in various combinations. Associations between certain symptoms and reactions to selective serological or molecular markers are reported.